1. Field of the Invention
This invention relates to an image forming optical apparatus in which face scanning is effected by slit exposure in a copier or the like, and particularly, to an image forming optical apparatus which uses an array of Dachmirror lenses.
2. Description of the Prior Art
An array of Dachmirror lenses has been known, which comprises a combination of a row composed of a plurality of lenses 10 and a corrugated reflecting surface 11 provided behind said row, as shown in FIG. 1. This can be used, for example, in a copying machine in which light from a light source 20 is reflected at an original surface 21, and said light is deflected towards a Dachmirror lens system 23 by a reflecting means 22 to form a latent image on a photosensitive drum 24, as shown in FIG. 2.
At this time, exposure is carried out through a slit 25. The width of the slit 25 and the position of slit relative to the Dachmirror lens system are important elements which control irradiance and an unevenness in irradiance at the time of exposure. However, sufficient studies have not yet been made on this respect.